286 Bulletin American Museum of Natural History [Vol. LIIL 
but they state that the only constant spiral is that at the periphery. 
Their statement ‘‘ Nous possédons toute la série des formes intermédiaires 
entre cette variété et le type de l’espéce,”’ could not be made of the Stan- 
leyville series, in which the two forms, if interbreeding as we suppose,! 
show remarkably complete segregation and remarkably few blends. 
This is true even of quite young specimens, which are decidedly more 
slender in spolzata, as will be seen by the measurements: 
Fig. 1f, ponthiervillensis: length, 14.7 mm.; diameter, 9.3 mm.; aperture, 8.8 
mm.; 3 whorls. 
Fig. 2d, spoliata: length, 14.7 mm.; diameter, 7.3 mm.; aperture, 7.3 mm.; 4 
whorls. 
Potadoma superba, new species 
Plate XXV, Figures 3-8e 
Stanleyville in an affluent of the Tshopo River; also in the Tshopo 
River (H. Lang and J. Bequaert Coll.). 
The shell is large, solid, turrited, with the last whorl somewhat swollen, burnt 
umber. The upper whorls are smoothish, rather weakly convex (in .well-preserved 
and young examples showing a sculpture of impressed spiral lines cutting fine, weak 
axial ripples, as in P. mungwana). On the third whorl from the base two spiral cords 
arise, rapidly becoming raised into spiral carine, of which there are four on the last 
whorl, with a small or indistinct fifth around the columella. The crest of the fourth 
carina is somewhat waved or lobed. The aperture is widely ovate, dirty whitish oTay 
with some brown stains within. The outer lip is strongly notched by the external 
carine, and is more or less produced, spout-like at the base, but this feature varies in 
different individuals. Columella has a rather strong callus, thickened locally near the 
posterior angle of the mouth. 
Length, 46.0 mm.; diameter, 20.0 mm.; about 444 whorls remaining. Type. 
Oh AS ig 20.0 3 % tf 
This fine species has some resemblance to P. tornata (v. Martens) 
of the Ituri head waters; but that has a less elongate spire and differs 
in details of sculpture. The most closely related species is P. ponthier- 
villensis (Dupuis and Putzeys), which differs by having shortly scaly 
nodes on the spiral keels, the upper keel being nearer to the suture. 
Usually the spire is relatively shorter in ponthiervillensis. 
There is some variation in the sculpture. In some specimens the 
second or intermediate keel arises at the end of the penult whorl, those 
above showing two keels; but in others it may arise a whorl earlier, 
SSS a oe et 
__ In one of the lots spoliata was preserved with ponthiervillensis. Whether taken together or in 
different colonies we do not know. The question whether the two forms occupy different ecologic sta- 
tions should be taken up by an observer on the spot. 
The lot from a brook near the Falls contained only spoliata, but included a specimen or two having a 
knotted upper spiral cord. 
